This invention relates generally to gas turbine rotor assemblies and more particularly to a blade retention apparatus for a gas turbine engine rotor assembly.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In a turbofan engine, which typically includes a fan placed at the front of the core engine, a high pressure turbine powers the compressor of the core engine. A low pressure turbine is disposed downstream from the high pressure turbine for powering the fan. Each turbine stage commonly includes a stationary turbine nozzle followed in turn by a turbine rotor.
A turbine rotor comprises a row of rotor blades mounted to the perimeter of a rotor disk that rotates about the centerline axis of the engine. Each rotor blade typically includes a shank portion having a dovetail for mounting the blade to the rotor disk and an airfoil that extracts useful work from the hot gases exiting the combustor. A blade platform, formed at the junction of the airfoil and the shank portion, defines the radially inner boundary for the hot gas stream. The turbine nozzles are usually segmented around the circumference thereof to accommodate thermal expansion. Each nozzle segment has one or more nozzle vanes disposed between inner and outer bands for channeling the hot gas stream into the turbine rotor.
To improve turbine engine performance, flowpath temperatures and blade tip speeds are increased. These conditions increase centrifugal loads and metal temperatures, requiring robust turbine blade and blade retainer designs. Rotor cavities are shielded from flowpath temperatures by overlap seals, formed by a combination of sealing flanges, often referred to as “angel wings”, which are mounted on the blades, blade retainers, or stator. This configuration isolates flowpath gas ingestion to one or more buffer cavities. In addition, cooler higher-pressure air from inside is introduced radially outward into the buffer cavities to mix with and to purge the higher temperature gases out of the cavity. The outermost overlap is located on a rotating turbine blade with the inboard overlap located on a static nozzle. These components are made from materials capable of withstanding higher temperatures. The innermost overlap is located on a rotating cooling plate that is made from a material with a lower temperature capability. The cooling plate, however, must extend into the higher temperature zone of the buffer cavity in order to provide sealing and axial retention of the turbine blades, and is often limited by the temperature capability of the material requiring an increased supply of cooler air. This increased cooling air flow directly impacts performance.
Accordingly, there is a need for a turbine blade retainer which is suitable for high temperature operation.